Hereditary deficiency of alpha 1 antitrypsin, the main serum inhibitor of proteolytic enzymes is associated with pulmonary emphysema of early onset. A multicentre survey of this disorder was started in 1976 and details of 166 subjects homozygous for the Z phenotype form the main body of this report. There were 126 index cases who were identified through chest clinics and 40 non-index cases who were identified through family studies. The index cases and many of the non-index cases had severe radiological and physiological abnormalities. A history of cigarette smoking had a significant effect upon the prognosis, but sex and occupational exposure to dust or fumes did not. There was a wide variance in lung function even among those who had never smoked.